Violation of spin conservation is likely to be a normal occurrence for reactions that satisfy the following criteria: (1) the reaction rate is limited by the rate of capture over a long-range centrifugal barrier in an attractive potential; (2) product formation is the result of fast rearrangement of a bound collision complex; and (3) attractive short-range potentials exist for more than one spin state of the complex. An analogy exists between the time evolution of the system during a reaction of this type and the optical phenomenon of quantum beats. Taking failure of spin-conservation into account removes some of the problems encountered in a previous calculation of the rate constant for reaction of CN with O-2 at very low temperatures. Problems encountered at very high temperatures suggest that this reaction system is too small for the decay of the NCOO* complex to be treated statistically.